Hydroprocessing can include processes which convert hydrocarbons in the presence of hydroprocessing catalyst and hydrogen to more valuable products. Hydrocracking is a hydroprocessing process in which hydrocarbons crack in the presence of hydrogen and hydrocracking catalyst to lower molecular weight hydrocarbons. Depending on the desired output, a hydrocracking unit may contain one or more fixed beds of the same or different catalyst. Slurry hydrocracking is a slurried catalytic process used to crack residue feeds to gas oils and fuels.
Hydroprocessing recovery units typically include an array of separators for cooling and depressurizing hydroprocessed effluent and separating gaseous streams from liquid streams and a stripping column for stripping hydroprocessed liquid with a stripping medium such as steam to remove unwanted hydrogen sulfide. The stripped stream then is typically heated and fractionated in a product fractionation column to recover products such as naphtha, kerosene and diesel. Lighter hydrocarbons may be recovered from a condensed overhead stream.
In a refinery, hydrogen has a prime importance and recovery of hydrogen improves refinery profitability significantly. Pressure swing absorption (PSA) units are useful for purifying hydrogen by adsorbing larger molecules from the hydrogen stream at high pressure and then releasing the larger molecules at swing to lower pressure to provide a tail gas stream.
In many regions liquefied petroleum gas (LPG) is also important for petrochemical and fuel uses and additional recovery of LPG can also boost profit. Naphtha is also useful for fuel and petrochemical feed stock and its further recovery is desirable.
There is a continuing need, therefore, for improved methods of recovering hydrogen, LPG and naphtha from hydroprocessed effluent streams.